The present invention relates generally to automatic decapsulators and more particularly to the decapsulation gaskets utilized in such decapsulators.
Automatic decapsulators are used to expose the die in any plastic package or device by an etching away the die""s plastic covering. Either fuming sulfuric, fuming nitric, or mixed filming nitric and sulfuric acids may be used as an etchant. Decapsulation is a fast and safe process that produces a clean, uncorroded die surface. When fuming nitric acid is used as the etchant, there is little or no damage to the die surface or bond pads. Fuming sulfuric acid is normally used at an elevated temperature to remove the plastics that are not compatible with fuming nitric acid. The etching process is performed under pressure in an inert atmosphere to reduce metal oxidation and to reduce the production of harmful fumes.
FIG. 1a illustrates a side view of a typical system for automatic decapsulation of a device. The system 10 includes a safety cover 11 which is coupled to an etch plate 13. The system 10 also includes a positioning fixture 12 coupled to the etch plate 13 which is typically metal and is aligned with a package 16 and a gasket 14, typically made of rubber. The gasket 14 is positioned under the device 16 with an etch window in the gasket""s center. The etchant is provided through the etch window to the device 16 via the etch head 18. Referring now to FIG. 1b, a top view of the conventional system is shown. As is seen, the fixture 12 and the gasket 14 must be aligned to etch the device 16 properly.
For many current plastic packages, such as plastic ball grid array (PBGA) or fine ball grid array (FBGA) packages, the plastic materials can only be removed using fuming sulfuric acid at a high temperature ( greater than 200xc2x0 C.). The etch time can be very long ( greater than 500 seconds) for some large size packages. Serious problems can occur while decapsulating a PBGA or FBGA package. First, the rubber gasket, which provides the etch window and seals the device to the etch head, distorts slightly when the rubber gasket is compressed between the device and the etch head. As a result, the etchant can attack areas not intended to be etched. With large devices, this slight distortion is not a concern, however, with small FBGA packages (which can be as small as 5 mmxc3x975 mm), the slight distortion in the etch window causes over etching, which in turn leads to an accumulation of etching acid at the package edges. This accumulation can wreck havoc because the back side of a PBGA or FBGA package generally contains a printed circuit board (xe2x80x9cPCBxe2x80x9d) substrate and solder ball connections. The excess acid at the package edge can creep to the backside of the package, ruining the PCB substrate and solder ball connections on the package.
Second, because the device sits directly on the rubber gasket, which is usually soaked with etching acid during decapsulation, the PCB substrate of the package can corrode. Finally, because the decapsulation temperature exceeds the melting point of the solder balls on the backside of the package, the solder balls can be smashed by the protection plate, which rests on the backside of the package. For the reasons discussed above, conventional decapsulation systems utilizing a rubber gasket are not feasible for PBGA and small FBGA packages. What is needed is a system and method to overcome the above-identified problems.
An automatic decapsulation system for a device is disclosed. The system comprises an etch plate, an etch head, an acid resistant and high heat endurance sheet, and a rubber gasket disposed between the etch head and the acid resistant and high heat endurance sheet. The sheet and rubber gasket combination provide a tight seal between the device and the etch head, and a precise etch window that does not deform during decapsulation. Moreover, the sheet automatically aligns the etch window with the device, thereby reducing the amount of time taken to otherwise align the gasket. In a preferred embodiment of the present invention, the system includes a device securing unit to secure the device without damaging the backside of the package.
A system in accordance with the present invention utilizes an acid resistant and high heat endurance sheet coupled with a rubber gasket to seal the device for decapsulation and to provide a well-defined etch window. In addition, the sheet/rubber gasket combination is also utilized as the fixture, thereby eliminating the need to align the gasket to the metal fixture utilized in the conventional system.